Acetolactate synthase (ALS) or acetohydroxyacid synthase (AHAS) is the first enzyme in the biosynthetic pathway of the branched chain amino acids valine, leucine and isoleucine in plants and microorganisms. Five distinct families of compounds inhibit the AHAS enzyme and are used as non-selective, broad-spectrum herbicides: sulfonylureas (SUs), imidazolinones (IMIs), triazolopyrimidines (TPs), sulfonylaminocarbonyltriazolinones (SCTs) and pyrimidinyloxybenzoates (POBs).
Given their high effectiveness and low-toxicity, certain herbicides are favored for agricultural use. However, the ability to use some of these herbicides in a particular crop production system depends upon the availability of resistant varieties of the crop plant of interest. To produce such resistant varieties, plant breeders need to develop breeding lines with the resistance traits. Accordingly, herbicide resistant breeding lines and varieties of crop plants, as well as methods and compositions for the production and use of resistant breeding lines and varieties, are needed.